Schedule II, Valuation and Qualifying Accounts (Details) - Allowance for Bad Debts - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at Jan. 1	$ 6.4	$ 6.4	$ 5.9
Charged to costs and expenses	4.9	5.1	6.1
Charged to other accounts	1.0	1.2	0.9
Deductions from reserves	(6.7)	(6.3)	(6.5)
Balance at Dec. 31	$ 5.6	$ 6.4	$ 6.4